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From:   Suren Baghdasaryan <surenb@google.com>
Date:   Thu, 7 Oct 2021 08:45:21 -0700
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Subject: Re: [PATCH v10 3/3] mm: add anonymous vma name refcounting
To:     Michal Hocko <mhocko@suse.com>
Cc:     David Hildenbrand <david@redhat.com>,
        John Hubbard <jhubbard@nvidia.com>,
        Pavel Machek <pavel@ucw.cz>,
        Andrew Morton <akpm@linux-foundation.org>,
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On Thu, Oct 7, 2021 at 12:59 AM Michal Hocko <mhocko@suse.com> wrote:
>
> On Wed 06-10-21 08:01:56, Suren Baghdasaryan wrote:
> > On Wed, Oct 6, 2021 at 2:27 AM David Hildenbrand <david@redhat.com> wrote:
> > >
> > > On 06.10.21 10:27, Michal Hocko wrote:
> > > > On Tue 05-10-21 23:57:36, John Hubbard wrote:
> > > > [...]
> > > >> 1) Yes, just leave the strings in the kernel, that's simple and
> > > >> it works, and the alternatives don't really help your case nearly
> > > >> enough.
> > > >
> > > > I do not have a strong opinion. Strings are easier to use but they
> > > > are more involved and the necessity of kref approach just underlines
> > > > that. There are going to be new allocations and that always can lead
> > > > to surprising side effects.  These are small (80B at maximum) so the
> > > > overall footpring shouldn't all that large by default but it can grow
> > > > quite large with a very high max_map_count. There are workloads which
> > > > really require the default to be set high (e.g. heavy mremap users). So
> > > > if anything all those should be __GFP_ACCOUNT and memcg accounted.
> > > >
> > > > I do agree that numbers are just much more simpler from accounting,
> > > > performance and implementation POV.
> > >
> > > +1
> > >
> > > I can understand that having a string can be quite beneficial e.g., when
> > > dumping mmaps. If only user space knows the id <-> string mapping, that
> > > can be quite tricky.
> > >
> > > However, I also do wonder if there would be a way to standardize/reserve
> > > ids, such that a given id always corresponds to a specific user. If we
> > > use an uint64_t for an id, there would be plenty room to reserve ids ...
> > >
> > > I'd really prefer if we can avoid using strings and instead using ids.
> >
> > I wish it was that simple and for some names like [anon:.bss] or
> > [anon:dalvik-zygote space] reserving a unique id would work, however
> > some names like [anon:dalvik-/system/framework/boot-core-icu4j.art]
> > are generated dynamically at runtime and include package name.
> > Packages are constantly evolving, new ones are developed, names can
> > change, etc. So assigning a unique id for these names is not really
> > feasible.
>
> I still do not follow. If you need a globaly consistent naming then
> you need clear rules for that, no matter whether that is number or a
> file. How do you handle this with strings currently?

Some names represent standard categories, some are unique. A simple
tool could calculate and report the total for each name, a more
advanced tool might recognize some standard names and process them
differently. From kernel's POV, it's just a name used by the userspace
to categorize anonymous memory areas.

>
> --
> Michal Hocko
> SUSE Labs